This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-212596, filed Jul. 12, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a key input device for use in, in general, personal computers, and more particularly to a keyboard with a Braille input function.
2. Description of the Related Art
Input devices that enable optically inconvenienced people to execute, by a Braille input operation, an input operation for an information processing apparatus such as a personal computer have been developed so far. As such an input device, a key input device is used in which some of the key switches arranged on a keyboard are assigned as Braille input function keys. A six-point or eight-point input system, in which six or eight keys assigned are simultaneously operated, is well known as a Braille input system.
A key input device having a Braille input function has been proposed in which information input using the Braille input function can be confirmed (see Jpn. Pat. Appln. KOKAI Publication No. 6-119094). Further, a key input system has been proposed which has a function for switching its input mode between a normal input mode for executing a normal character input operation, and a Braille input mode for executing a Braille input operation (see Jpn. Pat. Appln. KOKAI Publication No. 10-289051).
Moreover, a keyboard called a xe2x80x9cplain keyboardxe2x80x9d, which is effective for cost reduction, has been recently developed. In this keyboard, a diode and resistor are not provided for each key switch in a key matrix. In the structure, more than two keys cannot be simultaneously operated. If three or more keys are simultaneously operated, a phenomenon called a xe2x80x9ckey ghostxe2x80x9d occurs.
Referring to FIG. 4, a brief description will be given of the occurrence of the key ghost.
FIG. 4 shows a so-called scan-type keyboard. In the scan type, scan lines 40 are driven in units of lines at low level (L level), and the state of each return line 41 (high or low level) is read, thereby detecting (scanning) the operation (pushing) of each key.
Suppose that keys xcex1, xcex2 and xcex3 are simultaneously pushed (are in the ON state). At this time, if the scan lines for keys xcex1 and xcex4 are scanned, a so-called current-wraparound occurs, with the result that the key xcex4 is detected to be pushed (operated), although it is not actually pushed. This phenomenon will be called a xe2x80x9cghostxe2x80x9d.
In summary, where a key input device having a Braille input function is realized using a plane keyboard, if a Braille input operation is executed by simultaneously pushing three or more keys, a ghost key occurs to thereby cause an erroneous input operation.
It is an object of the present invention to provide a key input device capable of realizing both a usual key input operation and a reliable Braille key input operation even if the key input device is realized by a plane keyboard.
According to one aspect of the present invention, there is provided a key input device including facilities to avoid a ghost key operation during a Braille input operation.
The key input device comprises:
a plurality of key switches, predetermined ones of the key switches being assigned as both Braille input function keys and usual input function keys; and
a key switch circuit configured as a key matrix including row lines and column lines connected to the key switches, each of the predetermined key switches generating no ghost key when the predetermined key switches are simultaneously operated.